Hospital and field treatment and prevention of diarrhea and malnutrition, using Pediatric Nurse Practitioners and community health aides. Metabolic balance studies of sodium retention, protein quality, amino acid requirements. Serum proteins and albumin, plasma amino acids, creatinine excretion and hair root morphology as indicators of protein status. Ecology of malnutrition and its long-term effects by longitudinal study of malnourished infants, their so-called healthy siblings, and their truly healthy siblings. Hormonal levels and production in healthy, severely malnourished, and convalescent infants (GH, insulin, thyroid, TSH, cortisol, aldosterone, catecholamines). Role of Cu in Fe metabolism (infusion of ceruloplasmin and Cu acetate in Cu-deficient infants, disappearance of parenteral Fe in Cu-deficient). Incidence of lactase deficiency by race and age in U.S. and Peru; possible induction of lactase activity in apparently deficient; metabolic consequences of low lactase activity; effect of other diet ingredients on lactose tolerance. Effect of protein concentration and distribution (relative to calories) on utilization.